I just got a Tetra Whisper submersible heater for my 10 gallon. It has an adustable temperature nob on top ( + and -). I'm not sure if it is working correctly because the orange light to indicate it is working will just flicker on and off randomly, I'm not sure if it is supposed to do this or not. anyone familar with these heaters? I'm thinking about taking it back to wal-mart, it didn't come with a instruction manual like it should have either.

if the light means it is turned on then when the light is off it turns itself off. Heaters are not supposed to stay on all the time or else the water would get really hot. Once the heater senses the water has gotten to the temp. you told it to it will turn itself off then turn on again when it senses the temp. has dropped._________________

The little light, as you put it, is actually the heater core's 'pilot' light...it merely tells you the heater core is 'active' and currently adjusting the water temperature to the level set on the adjustable knob. they are a little tricky to use, but once you get the water to a stable temperature, don't move the knob!